diff --git a/chacha20poly1305/chacha20poly1305_amd64.go b/chacha20poly1305/chacha20poly1305_amd64.go
index ae73973ae3..f0d34856b2 100644
--- a/chacha20poly1305/chacha20poly1305_amd64.go
+++ b/chacha20poly1305/chacha20poly1305_amd64.go
@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// +build amd64
+// +build amd64,go1.7
 
 package chacha20poly1305
 
diff --git a/chacha20poly1305/chacha20poly1305_amd64.s b/chacha20poly1305/chacha20poly1305_amd64.s
index 7469667e64..ca9974f9a7 100644
--- a/chacha20poly1305/chacha20poly1305_amd64.s
+++ b/chacha20poly1305/chacha20poly1305_amd64.s
@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
+// +build go1.7
+
 #include "textflag.h"
 // General register allocation
 #define oup DI
diff --git a/chacha20poly1305/chacha20poly1305_noasm.go b/chacha20poly1305/chacha20poly1305_noasm.go
index 495843adae..1d4dcd33fd 100644
--- a/chacha20poly1305/chacha20poly1305_noasm.go
+++ b/chacha20poly1305/chacha20poly1305_noasm.go
@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// +build !amd64
+// +build !amd64 !go1.7
 
 package chacha20poly1305
 
diff --git a/poly1305/sum_amd64.go b/poly1305/sum_amd64.go
index 4dd72fe799..1501f13909 100644
--- a/poly1305/sum_amd64.go
+++ b/poly1305/sum_amd64.go
@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// +build amd64,!gccgo,!appengine
+// +build amd64,!gccgo,!appengine,go1.7
 
 package poly1305
 
diff --git a/poly1305/sum_amd64.s b/poly1305/sum_amd64.s
index bc75c61afc..56e8311c8d 100644
--- a/poly1305/sum_amd64.s
+++ b/poly1305/sum_amd64.s
@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// +build amd64,!gccgo,!appengine
+// +build amd64,!gccgo,!appengine,go1.7
 
 #include "textflag.h"
 
diff --git a/poly1305/sum_ref.go b/poly1305/sum_ref.go
index 0b24fc78b9..5d25a566ea 100644
--- a/poly1305/sum_ref.go
+++ b/poly1305/sum_ref.go
@@ -2,7 +2,7 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// +build !amd64,!arm gccgo appengine
+// +build !amd64,!arm gccgo appengine !go1.7
 
 package poly1305